1. Field of the Invention
This invention relates to a process for eluting indium from a chelate resin adsorbing indium. More particularly, the invention relates to a process for selective elution of indium which comprises firstly eluting cationic metals other than indium preferentially from a chelate resin having a phosphorus atom-containing, chelate-forming group which contains said metals including indium adsorbed and then eluting indium.
2. Description of the Prior Art
As a process for recovering indium from an indium-containing solution obtained by subjecting a sludge as a by-product in refining of zinc, lead or the like to a treatment such as leaching by sulfuric acid, there has hitherto been known a process for recovering indium by allowing a chelate resin having a functional group of iminodiacetic acid type to adsorb the indium in the solution [Anal. Chem. Acta., 40 (1968) 479-485]. However, because such a chelate resin has low adsorptivity for indium, the recovery amount of indium per unit amount of chelate resin used is low. For improvement of this problem, the present inventors had previously proposed a process for recovering indium by the use of a chelate resin having a phosphorus atom-containing, chelate-forming group [Japanese Patent Application Kokai (Laid-open) No. 172256/1983]. This chelate resin has much higher adsorptivity for indium. However, the resin, similarly to other known chelate resins, simultaneously adsorbs other metals such as, for example, iron, zinc, nickel, cobalt, copper and the like together with indium; accordingly, when an indium-containing solution wherein these other metals are also present is subjected to adsorption by the resin, the other metals are also adsorbed; and, in elution of indium from the resin by the use of an eluent, the other metals are eluted together with indium.
Because of the above problem, in recovery of indium from an indium-containing eluate obtained as above, a very complicated refining process has been required such as (1) a process wherein said eluate is neutralized to precipitate indium and other metal ions in the form of hydroxide and the hydroxides are dissolved in an acid or an alkali and this step is repeated to gradually increase the concentration of indium and (2) a process wherein said eluate is subjected to extraction by an indium-extracting agent and then the resulting extract is subjected to back extraction by a back extracting agent.
In view of the above situation, the present inventors have made extensive study on a process for selectively eluting and separating indium from a chelate resin containing adsorbed indium which is obtained by contacting an indium-containing solution with a particular chelate resin having a phosphorus atom-containing, chelate-forming group, of high adsorptivity for indium. As a result, it has been found that indium can easily be isolated from said chelate resin containing adsorbed indium by a two step treatment which comprises firstly contacting the chelate resin with a particular primary eluent capable of preferentially eluting metals other than indium and then contacting the resulting resin with an eluent for indium capable of eluting indium. Based on this finding, the present invention has been completed.